Chlorinated hydrocarbon by-product materials are generated in a wide variety of chlorinated hydrocarbon manufacturing operations, such as the manufacture of ethylene dichloride, vinyl chloride monomer, methyl chloroform, trichloroethylene, perchloroethylene, allyl chloride or mono and dichlorobenzene. These are all commercial products, some of which may be used as solvents, others as feedstocks for producing materials such as non-ozone depleting refrigerants, plastic film (Saran Wrap.RTM.), polyvinyl chloride, Teflon.RTM., or Kynar.RTM.. The chlorinated hydrocarbon by-products of these manufacturing operations have been traditionally considered hazardous wastes requiring carefully regulated treatment. One common method for treating these hazardous by-products is to destroy them in a chlorinated hydrocarbon waste incinerator. In such systems, the liquid wastes are injected into a natural-gas fired incinerator, where the chlorinated organic molecules are essentially oxidized, thus yielding hydrogen chloride (HCl), salt water and a vent gas comprised mostly of nitrogen and carbon dioxide. An example of this type of system is depicted in FIG. 1.
Steam, or perhaps water, that is sometimes used to cool the reaction in these incinerators mixes with the hydrogen chloride, thus yielding a weaker hydrochloric acid by-product solution. This hydrochloric acid by-product, from four to twenty (4% to 20%) percent by weight hydrogen chloride, is too weak for typical commercial uses, which generally require acid strengths in excess of thirty-one (31%) percent by weight hydrogen chloride. Therefore, the useless hydrochloric acid by-product must be neutralized and disposed of as salt-water waste. Under federal guidelines, any unit producing an acid stream greater than three (3%) percent by weight hydrogen chloride must be classed as a halogen acid furnace (HAF) under the General Hazardous Waste Rules. This weak acid stream is therefore considered an undesirable waste product. Furthermore, the pre-dominately nitrogen/carbon dioxide waste gas generated in these incinerators is simply vented into the atmosphere. Some of the components present in the incinerator may also be converted into extremely toxic dioxin and into nitrous oxide, which may then appear in the vent gases. The fact that all by-products of the typical chlorinated hydrocarbon incineration unit are un-useful, undesirable waste materials represents a disadvantage to this system.
The valorization of chlorinated residuals (VCR) process unit, similar to the incinerator described above, was designed specifically to produce at least one useful by-product of the typical chlorinated hydrocarbon oxidation technique that takes place in an incinerator, namely anhydrous hydrogen chloride, although, of course the principles of the invention are applicable to other types of processes as well, including new facilities which are designed from the beginning to use the principles of the present invention. However, for exemplary purposes, the invention will be primarily discussed with respect to the particular BCP VCR facility described more fully below.
The VCR process unit, as employed by Borden Chemicals and Plastics (BCP) at Geismar, L A, converts the chlorinated hydrocarbon by-product left over from the manufacture of vinyl chloride monomer into useful hydrogen chloride. One method for producing vinyl chloride monomer (VCM) entails reacting acetylene and anhydrous hydrogen chloride (HCl) as the raw materials for manufacturing the VCM product (see FIG. 2). This process, as practiced by BCP, is termed the VCM-A Process. Another method for producing VCM entails reacting chlorine or anhydrous HCl and ethylene to produce ethylene dichloride or 1,2 dichloroethane (EDC). The EDC is then thermally reacted to produce VCM (see FIG. 3). This process, as practiced by BCP, is termed the VCM-E Process. In both VCM processes, the chlorinated hydrocarbon by-product, also called organic intermediate materials, is generated. These organic intermediate materials consist primarily of the following chemical components:
ethylene dichloride (CH.sub.2 ClCH.sub.2 Cl), trichloroethane (CHCl.sub.2 CH.sub.2 Cl), 1,1,2,2 tetrachloroethane (CHCl.sub.2 CHCl.sub.2), 1,1,1,2 tetrachloroethane (CHCl.sub.3 CH.sub.2 Cl), and pentachloroethane (CHCl.sub.2 CCl.sub.3) PA1 a) The materials would be used in total to produce feedstocks that would be further used to produce other marketable products. The production of water and a very miner amounts of salt is acceptable. The key is to convert essentially all the carbon, chloride and hydrogen contained in the chlorinated hydrocarbon by-products into useful HCl and useful CO.sub.2. PA1 b) No stream would be produced that contained more than three (3%) by weight HCl in water. If a stream is produced having three (3%) percent or more by weight of HCl in water, the process as defined in the RCRA regulations is classified as halogen acid furnace and all materials so processed is subject to a hazardous waste tax. With no acid produced containing greater than three (&gt;3%) percent HCl in water, the modified VCR process unit can not be classified as a halogen acid furnace. PA1 c) There would be no vents to the atmosphere. With the absorbent beds removing water and any possible contaminants from the CO.sub.2 product and those contaminants ultimately being recycled back into the VCR reactor, there is zero discharge to the environment of such things as dioxin. The outstanding thing about the process is that what is now considered very hazardous chlorinated hydrocarbon waste would be processed in a manner such that the environmental impact would be zero. PA1 a) The materials would be used in total to produce feedstocks that would be further used to produce other marketable products. The production of water and a very miner amounts of salt is acceptable. The key is to convert essentially all the carbon, chloride and hydrogen contained in the chlorinated hydrocarbon by-products into useful HCl and useful CO.sub.2. PA1 b) No stream would be produced that contained more than three (3%) percent by weight HCl in water. If a stream is produced having three (3%) percent or more by weight of HCl in water, the process as defined in the RCRA regulations is classified as halogen acid furnace and all materials so processed is subject to a hazardous waste tax. With no acid produced containing greater than three (&gt;3%) percent HCl in water, the modified VCR process unit can not be classified as a halogen acid furnace. PA1 c) There would be no vents to the atmosphere. With the absorbent beds removing water and any possible contaminants from the CO.sub.2 product and those contaminants ultimately being recycled back into the VCR reactor, there is zero discharge to the environment of such things as dioxin. The outstanding thing about the process is that what is now considered very hazardous chlorinated hydrocarbon waste would be processed in a manner such that the environmental impact would be zero.
Compounds such as chloroprene, 1,1 dichloroethane, 1,1,1 trichloroethane, chloroform, carbon tetrachloride, cis/trans-dichloroethylene, trichloroethylene, perchloroethylene and various other chlorinated organic compounds are also possible intermediate materials. These organic intermediate materials are further used as feedstock in the VCR process unit, whereby anhydrous HCl is manufactured for use as a raw material feedstock for the VCM-A process described above. The VCR process unit therefore serves as an HCl manufacturing unit using as feedstock the organic intermediate materials produced in the VCM-A and VCM-E processes, the intention being to maintain a "closed-loop" manufacturing process whereby all intermediate materials are usefully and beneficially utilized.
Thus, the VCR process unit is designed specifically to use the organic intermediate by-product of both VCM processes as a feedstock for manufacturing HCl, a necessary raw material in the VCM-A and VCM-E processes. The reaction taking place in the VCR process unit is depicted in FIG. 4. The system itself is depicted in FIG. 5.
The VCR process unit uses two raw materials for manufacturing HCl, namely the organic feedstock and air. These raw materials are mixed in the VCR reactor, which contains a proprietary mixing device in which HCl is initially manufactured. In this mixing device, vaporized liquid feedstock is introduced into a high velocity, high temperature air stream. The feedstock and the air react to form anhydrous HCl. The type of reactions that occur in the VCR process are represented by the following equation: EQU CH.sub.2 ClCH.sub.2 Cl+CHCl.sub.2 CH.sub.2 Cl+4.5O.sub.2 +N.sub.2 --5HCl+4CO.sub.2 +H.sub.2 O+N.sub.2
From the VCR reactor, the anhydrous HCl is directed into a purification unit and then used as feedstock in the VCM-A process. Excess water generated in the reactor must be purged from the system via this HCl purification unit. Since this purge water contains greater than three (3%) percent by weight hydrogen chloride, thus constituting a weak acid stream, the VCR process unit is also classed as a halogen acid furnace. This weak acid purge must be neutralized to form salt water, which may then be sewered.
Meanwhile, a gaseous by-product, comprised mainly of CO.sub.2, N.sub.2, and minimal amounts of O.sub.2, HCl and Cl.sub.2, is directed into an alkaline-fed scrubbing unit, where any HCl and chlorine molecules are converted into salt water and then disposed of. Remaining gases, comprised mainly of CO.sub.2, N.sub.2 and minimal amounts of O.sub.2, are vented to the atmosphere.
The VCR process unit attempts to achieve "closed system" status for the VCM manufacturing process by converting the chlorinated organic material into reusable HCl. The remaining by-products, such as the salt water created from the neutralization of the weak acid purge from the HCl purification unit or from the alkaline-fed scrubbing unit, or the gaseous vent emissions comprised of CO.sub.2, N.sub.2, O.sub.2 have been historically considered environmentally harmless and thus suitable for release into the environment. However, recent concern about global warming and the need to reduce emissions of CO.sub.2, a greenhouse-effect gas, has prompted the U.S. EPA to look with scrutiny on chemical processes that needlessly vent CO.sub.2 to the atmosphere.
Furthermore, the weak acid purge from the HCl neutralization unit is an undesirable waste product, as is the possible presence of dioxins inadvertently generated in the reactor that may appear in the vent gases.
A need exists, therefore, to modify the existing VCR process and the typical chlorinated hydrocarbon waste incinerator such that no CO.sub.2 is emitted to the atmosphere in the vent gas emissions from either system. The U.S. EPA, in carrying out the intentions and objectives of the Resource Conservation and Recovery Act (RCRA), has incorporated into the RCRA regulations certain rules and procedures to encourage chemical manufacturers to exploit as feedstocks for producing useful chemical products those intermediate materials that otherwise would be classified as hazardous waste materials. The EPA's ultimate goal is to achieve near one-hundred (100%) percent conversion of such intermediate materials into useful chemical products. This goal can be achieved by modifying existing chlorinated hydrocarbon waste incinerators and VCR process units such that no CO.sub.2 is emitted to the atmosphere because of the unnecessary introduction of N.sub.2 into the incinerator or the VCR. With no N.sub.2 being introduced into either system, the vent from both systems becomes reasonably pure, marketable CO.sub.2, thus enabling essentially one-hundred (100%) percent beneficial utilization of the chlorinated organic intermediates.
A need also exists to modify the anhydrous HCl purification unit attached to the VCR process unit such that the weak acid stream purged from the system contains three (3%) percent or less by weight hydrogen chloride. These modifications to the HCl purification unit are also applicable to those HCl purification units (herein termed "primary scrubbers") associated with chlorinated hydrocarbon waste incinerators.
A need further exists to modify the final gas vents in the VCR process unit and the chlorinated hydrocarbon waste incinerator such that undesirable compounds such as dioxins that might be present in the vent gases are captured before release to the atmosphere and destroyed within the system.